Aircraft damage (e.g. as a result of collision, bird strike or extreme weather;

Illegal activity (e.g. bomb-threat, wilful damage or hi-jacking).

An emergency or abnormal situation may result in it being impossible to continue the flight to destination as planned, resulting in one or more of the following outcomes:

Loss of altitude;

Diversion to a nearby aerodrome;

Forced landing.

Handling Emergency or Abnormal Situations

The operator shall provide operations staff and flight crew with an aircraft operating manual, for each aircraft type operated, containing the normal, abnormal and emergency procedures relating to the operation of the aircraft. The manual shall include details of the aircraft systems and of the emergency or abnormal checklist (EAC) to be used. The design of the manual shall observe Human Factors principles. (ICAO Annex 6 Part I: Operation of Aircraft, Chapter 6 Para 6.1.3)

An operator shall establish and maintain a ground and flight training programme, approved by the State of the Operator, which ensures that all flight crew members are adequately trained to perform their assigned duties. ... The training programme ... shall include proper flight crew coordination and training in all types of emergency or abnormal situations or procedures caused by powerplant, airframe or systems malfunctions, fire or other abnormalities. ... The training for each flight crew member, particularly that relating to abnormal or emergency procedures, shall ensure that all flight crew members know the functions for which they are responsible and the relation of these functions to the functions of other crew members. The training programme shall be given on a recurrent basis, as determined by the State of the Operator. (ICAO Annex 6 Part I: Operation of Aircraft, Chapter 9 Para 9.3.1)

In practice, immediate actions in response to certain emergency or abnormal situations (e.g. fire, engine failure or loss of pressurisation) are carried out from memory; action taken is then confirmed by reference to the EAC, which also contains subsequent action and considerations.

For ease of use, the EAC is normally contained in a separate volume from the Operations Manual, which may be referred to as the Quick Reference Handbook (QRH).